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Understanding s-shaped current-voltage characteristics in organic solar cells containing a TiOx interlayer with impedance spectroscopy and equivalent circuit analysis

: Ecker, B.; Egelhaaf, H.J.; Steim, R.; Parisi, J.; Hauff, E. von


Journal of physical chemistry. C, Nanomaterials and interfaces 116 (2012), Nr.31, S.16333-16337
ISSN: 1932-7447
ISSN: 1932-7455
Fraunhofer ISE ()

In this study we propose an equivalent circuit model to describe S-shaped current-voltage (I-V) characteristics in inverted solar cells with a TiOx interlayer between the cathode and the poly(3-hexylthiophene):[6,6]-phenyl C61 butyric acid methyl ester active layer. Initially the solar cells demonstrate S-shaped I-V characteristics resulting in a low fill factor (FF). Upon light soaking with UV radiation, the resistance of the TiOx interlayer decreases, the S-shape disappears, and the FF increases. Impedance spectroscopy was used to investigate the influence of the resistance of the TiOx layer on the shape of the I-V characteristics. We show that the equivalent circuit model can describe the voltage dependence of the data before and after light soaking in a range from -1 to +1.5 V well, demonstrating the robustness of the model. The equivalent circuit elements can be attributed to the distinct layers in the solar cell, therefore giving insight into the origin of the S-shape behavior in this solar cell architecture.